Persons who must work in high-level noise are subject to developing a noise-induced hearing loss. This loss will be permanent, irrecoverable, and handicapping in many individuals and may combine with hearing loss they acquire due to aging and medical conditions. Industry groups where workers are exposed to high-level noise are General Building Contractors, Special Construction Contractors, Lumber and Wood Products, Primary Metal Industries, Fabricated Metal Products, Transportation Equipment Manufacturers, and Mining. These workers must use some form of hearing protection to prevent noise-induced hearing loss. In many cases, however, the workers' safety also depends on their ability to communicate with each other. Given the choice between personal safety through effective communication and hearing preservation, many workers opt not to wear hearing protectors which also impair their ability to communicate.
In spite of the fact that the Occupational Safety and Health Administration (OSHA) requires the use of hearing protection for all individuals exposed to Time Weighted Averaged noise levels greater than 85 dBA, many workers refuse to use hearing protection. Most workers who object to using hearing protection say that it interferes with their ability to understand the speech of other workers and their own speech, particularly in noise. A system which allows workers to hear other workers' speech and their own in a natural sounding manner would effectively remove that objection. Many workers who now are resistant to using hearing protectors would probably want to use a system which both enhances their ability to understand speech in noise and protects their hearing as well.
Many systems exist which purport to allow workers to hear and understand each other and protect hearing, but these systems have not been widely accepted, for the following reasons.
1. Most systems are one-channel, simplex send/receive systems which rely upon the wearer to operate a switch or upon voice-activated transmit switches. In many situations a worker will not have hands free to operate a switch and will be working in noise levels so high as to make operation of a voice-activated switch unreliable. Such systems are manufactured and sold by David Clark, Howard Leight, and Telex. PA1 2. Systems with noise-canceling microphones mounted in front of the mouth, outside the earmuffs, must highly filter the speech and noise to improve the signal-to-noise ratio. This results in a very unnatural, tinny sound, which can be irritating to listen to. Such systems are also manufactured and sold by David Clark, Howard Leight, and Telex. PA1 3. Systems which place speech pickup systems mounted inside earplugs or under earmuffs, the pickup being either an acoustic microphone or a vibration sensors, do not process the speech to restore the natural mouth-to-ear acoustic transfer function which accounts for how speakers perceive their own speech. This lack of processing results in speech which sounds muffled and is difficult to understand under most conditions. Such systems are manufactured and sold by Maxtron and Archer. PA1 4. Systems which place microphones inside earplugs or under earmuffs have used microphones which are not bi-polar and which are not capable of handling high-levels of speech input. Thus, the speech picked up is distorted prior to transmission. Such systems are manufactured and sold by Maxtron and Archer. PA1 5. Systems which are incorporated into noise-reducing earmuffs have used microphones or bone-conduction pickups which must be inserted into the ear canal before the earmuff is fitted over the ear. Thus, the wearer must tolerate the relatively cumbersome task of correctly inserting the pickup transducer before correctly putting on the earmuff. This often results in incorrect wearing of the earmuff, reduced sound attenuation from the earmuff, and increased risk of noise-induced hearing loss for the wearer.